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Appendix D VMS Language Extensions
This chapter describes the VMS language extensions that Sun Fortran 77 supports. These extensions are all, of course, nonstandard. @
Background
This FORTRAN compiler includes the VMS extensions to make it as easy as possible to port FORTRAN programs from VMS environments to Solaris environments. The compiler provides almost complete compatibility with VMS FORTRAN. These extensions are included in dbx as well as f77.
VMS Language Features in Sun Fortran
This list is a summary of the VMS features that are included in f77. Details are elsewhere in this manual.
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Initialize in declarations
Initialization of variables in declaration statements is allowed. Example:
CHARACTER*10 NAME /'Nell'/
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Noncharacter format specifiers
If a runtime format specifier is not of type CHARACTER, the compiler accepts that too, even though the FORTRAN Standard requires the CHARACTER type.
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Omitted arguments in subprogram calls
The compiler accepts omitted actual argument in a subroutine call, that is, two consecutive commas compile to a null pointer. Reference to that dummy argument gives a segmentation fault.
The above statement is treated as follows:
X = A ** (-B)
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Illegal real expressions
When the compiler finds a REAL expression where it expects an integer expression, it truncates and makes a type conversion to INTEGER.
Examples: Contexts for illegal real expressions that f77 converts to integer:
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Alternate RETURN
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Dimension declarators and array subscripts
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Substring selectors
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Computed GO TO
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Logical unit number, record number, and record length
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Typeless numeric constants
Binary, hexadecimal and octal constants are accepted in VMS form.
Example: Constants-Binary (B), Octal (O), Hexadecimal (X or Z):
DATA N1 /B'0011111'/, N2/O'37'/, N3/X'1f'/, N4/Z'1f'/
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Function length on function name, rather than on the word FUNCTION
The compiler accepts nonstandard length specifiers in function declarations.
Example: Size on function name, rather than on the word FUNCTION:
INTEGER FUNCTION FCN*2 ( A, B, C )
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Alternate return
The nonstandard & syntax for alternate-return actual arguments is treated as the standard FORTRAN * syntax. Example
CALL SUBX ( I, *100, Z
) ! Standard
CALL SUBX ( I, &100, Z ) ! Nonstandard alternate syntax
:
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Direct I/O with 'N record specifier
The nonstandard record specifier 'N for direct-access I/O statements is accepted.
Example: A nonstandard form for record specifier:
READ ( K ' N ) LIST
The above is treated as:
READ ( UNIT=K, REC=N ) LIST
The logical unit number is K and the number of the record is N.
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Variable Expressions in FORMAT Statements
In general, inside a FORMAT statement, any integer constant can be replaced by an arbitrary expression; the single exception is the n in an nH edit descriptor. The expression itself must be enclosed in angle brackets.
Example: The 6 in the following statement is a constant:
1 FORMAT( 3F6.1 )
6 can be replaced by the variable N, as in:
1 FORMAT( 3F<N>.1 )
VMS Features Requiring -xl or -vax=spec
You get most VMS features automatically without any special options. For a few of them, however, you must add the -xl option on the f77 command line.
In general, you need this -xl option if a source statement can be interpreted for either a VMS way of behavior or an f77 way of behavior, and you want the VMS way of behavior. The -xl option forces the compiler to interpret it as VMS FORTRAN.
Note also the --vax=spec option, which allows specification of these VMS extensions individually. See the Fortran User's Guide for details.
Summary of Features That Require -xl[d]
You must use -xl[d] to access the following features:
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Unformatted record size in words rather than bytes (-xl)
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VMS-style logical file names (-xl)
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Quote (") character introducing octal constants (-xl)
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Backslash (\) as ordinary character within character constants (-xl)
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Nonstandard form of the PARAMETER statement (-xl)
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Debugging lines as comment lines or FORTRAN statements (-xld)
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Align structures as in VMS FORTRAN (-xl)
Details of Features That Require -xl[d]
Here are the details:
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Unformatted record size in words rather than bytes
In f77, direct-access, unformatted files are always opened with the logical record size in bytes.
If the -xl[d] option is not set, then the argument n in the OPEN option RECL=n is assumed to be the number of bytes to use for the record size.
If the -xl[d] option is set, then the argument n in the OPEN option RECL=n is assumed to be the number of words, so the compiler uses n*4 as the number of bytes for the record size.
If the -xl[d] option is set, and if the compiler cannot determine if the file is formatted or unformatted, then it issues a warning message that the record size may need to be adjusted. This result could happen if the information is passed in variable character strings.
The record size returned by an INQUIRE statement is not adjusted by the compiler; that is, INQUIRE always returns the number of bytes.
These record sizes apply to direct-access, unformatted files only.
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VMS-style logical file names
If the -xl[d] option is set, then the compiler interprets VMS logical file names on the INCLUDE statement if it finds the environment variable, LOGICALNAMEMAPPING, to define the mapping between the logical names and the UNIX path name.
You set the environment variable to a string of the form:
"lname1=path1; lname2=path2; "
Remember these rules for VMS style logical file names:
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Each lname is a logical name and each path1, path2, and so forth, is the path name of a directory (without a trailing /).
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For logical names, uppercase and lowercase are significant. If a logical name is encountered on the INCLUDE statement which is not specified in the LOGICALNAMEMAPPING, the file name is used, unchanged.
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Quote (") character introducing octal constants
If the -xl[d] compiler option is on, a VMS FORTRAN octal integer constant is treated as its decimal form.
Example: VMS octal integer constant:
JCOUNT = ICOUNT + "703
The above statement is treated as:
JCOUNT = ICOUNT + 451
If the -xl[d] option is not on, then the "703 is an error.
With -xl[d], the VMS FORTRAN notation "703 signals f77 to convert from the integer octal constant to its integer decimal equivalent, 451 in this case. In VMS FORTRAN, "703 cannot be the start of a character constant, because VMS FORTRAN character constants are delimited by apostrophes, not quotes.
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Backslash (\) as ordinary character within character constants
If the -xl[d] option is on, a backslash in a character string is treated as an ordinary character; otherwise, it is treated as an escape character.
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Nonstandard form of the PARAMETER statement
The alternate PARAMETER statement syntax is allowed, if the -xl[d] option is on.
Example: VMS alternate form of PARAMETER statement omits the parentheses:
PARAMETER FLAG1 = .TRUE.
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Debugging lines as comment lines or FORTRAN statements (-xld)
The compiler interprets debugging lines as comment lines or FORTRAN statements, depending on whether the -xld option is set. If set, they are compiled; otherwise, they are treated as comments.
Example: Debugging lines:
REAL A(5) / 5.0, 6.0, 7.0, 8.0, 9.0 /
DO I = 1, 5
X = A(I)**2
D PRINT *, I, X
END DO
PRINT *, 'done'
END
With -xld, this code prints I and X. Without -xld, it does not print them.
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Align structures as in VMS FORTRAN
Use this feature if your program has some detailed knowledge of how VMS structures are implemented. If you need to share structures with C, you should use the default: no -xl
Unsupported VMS FORTRAN
Most VMS FORTRAN extensions are incorporated into the f77 compiler. The compiler writes messages to standard error for any unsupported statements in the source file. The following is a list of the few VMS statements that are not supported.
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Some of the INCLUDE statement
Some aspects of the INCLUDE statement are converted. The INCLUDE statement is operating system-dependent, so it cannot be completely converted automatically. The VMS version allows a module-name and a LIST control directive that are indistinguishable from a continuation of a UNIX file name. Also, VMS ignores alphabetic case, so if you are inconsistent about capitalization, distinctions are made where none are intended.
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Getting a long integer--expecting a short
In VMS FORTRAN, you can pass a long integer argument to a subroutine that expects a short integer. This feature works if the long integer fits in 16 bits, because the VAX addresses an integer by its low-order byte. This feature does not work on SPARC systems.
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